1. Field of the Invention
The present invention relates to a method of discriminating pictures, whereby a picture is sorted and discriminated into regions of a line picture, a halftone dot picture and a continuous tone picture.
2. Description of the Prior Art
Methods presented in the following documents, for instance, are known as conventional methods of discriminating pictures.
(1) "Extraction of structural information in documentary pictures", Mitsuhiro Murao, Toshifumi Sakai, 1980, 21st National Meeting of the Information Processing Institute, 7H-1.
(2) "Real-time discrimination of halftone pictures in documentary pictures", Morizumi Kurose, Koichi Ejiri, Akira Sakurai, 1981, 23rd National Meeting of the Information Processing Institute, 6C-6.
(3) "Binary reproduction of documentary pictures including gradation regions", Hiroshi Makino, Yukihisa Akada, Shingakuron, (D)J65-D, 3, pp. 307.about.314, March, 1982.
(4) "Sorting of pictures by computer for compression coding", August, 1982, Shingakuron, (D)J65-D, 8, pp. 1018.about.1025.
(5) Japanese Patent Laid-Open No. 132061/1981, "Detecting system for dot picture signals".
(6) "Reproduction of values in newspaper halftone", Hiroshi Ueno, Takayoshi Semasa, Printing Magazine, 1983 (Vol. 66) 1, pp. 15.about.23.
(7) Japanese Patent Laid-Open No. 149674/1981, "Discriminating method of picture characteristics".
These conventional methods are intended mainly for discrimination between line pictures and continuous tone pictures, and between line pictures and a halftone dot pictures. In reality, however, the line picture, the halftone dot picture and the continuous tone picture may all exist simultaneously in most all complete pictures; therefore, a method of discriminating said three kinds of pictures is needed. From such a viewpoint, the present inventors proposed the method of discriminating the above three kinds of pictures in an article entitled "Study of picture discriminating method", in the Overall National Meeting of the Electronic Communication Institute, 1167. Said method, however, had a problem in that it tended to make an error in discrimination of a continuous picture in which density varied sharply.
In this relation, an article entitled "Recognition of rectangular fields in facsimile document and handwritten discrimination numbers therein", 12th Picture-Engineering Conference 7-2, is known as a proposal for a region-extracting method for extracting picture regions of the same kind from a picture. According to this method, first a picture is divided into small regions; then, it is binary-coded and thereafter the small regions in the entire picture are collected in a plurality of large rectangular regions. Next, each large rectangular region is divided into window regions, and the probability of occurrence of a black picture element and the local deviation thereof within a window are determined. In addition, the amount of data area-projected on coordinate axes (X, Y) is determined as peripheral distribution. Then, the attributes of "photograph", "drawing" and "writing" are discerned according to the probability of occurrence of the black picture element and the local deviation thereof within the window, and the periodicity of the peripheral distribution is checked. Based on the results of these processes, determination is made between "writing" and "drawing", and the extraction of regions is conducted.
This method, however, has problems that it is inadequate for coping with regions having arbitrary forms since the process of collecting regions in the large rectangular regions together is taken initially, and that the extraction of regions is difficult for a character unit having no periodicity. Thus, an art adaptable for any arbitrary form and picture ("picture" means not only a tonal image) has been wanted.